It depends what material you are using for your wall. If its a newer brick then use 5 sand and 1 cement, if its a reclaim or hand made brick you could use 5 sand, 1 cement and 1 lime and if its stone use 3 sharp sand, 3 sand, 1 cement and 1 lime (you should expose aggregate in the stone wall hence using some sharp sand).

You should also put some plasticiser (febmix) in any mix that doesnt contain lime to aid the playability of the mix.